1. Field of the Invention
The present invention relates to a method of manufacturing hexagonal ferrite magnetic particles and to the hexagonal ferrite magnetic particles obtained by the above method. More particularly, the present invention relates to a method of manufacturing hexagonal ferrite magnetic particles making it possible to provide microparticles by inhibiting the aggregation of particles in a step of ferritization by calcination, and to the hexagonal ferrite magnetic particles obtained by the above method.
The present invention further relates to usage of the above manufacturing method and hexagonal ferrite magnetic particles.
2. Discussion of the Background
Hexagonal ferrite is employed in permanent magnets. In addition, it has also been employed as a magnetic material in magnetic recording media in recent years.
The method (coprecipitation method) of ferritization by conducting calcination of a coprecipitate obtained by coprecipitating an iron salt and an alkaline earth metal salt is a known method of manufacturing hexagonal ferrite (see Japanese Unexamined Patent Publications (KOKAI) Heisei No. 7-172839 and No. 2010-1171, which are expressly incorporated herein by reference in their entirety). The method of obtaining a coprecipitate by forming a reverse micelle (reverse micelle method) has been proposed as an improved coprecipitation method (see Japanese Unexamined Patent Publication (KOKAI) No. 2007-91517, which is expressly incorporated herein by reference in its entirety). The application of the reverse micelle method to the manufacturing of ∈-iron oxide, employed as an electromagnetic wave absorber, is proposed in Japanese Unexamined Patent Publication (KOKAI) No. 2008-277726 or English language family member US2010/238063A1 and U.S. Pat. No. 8,072,365, which is expressly incorporated herein by reference in its entirety.
Due to the increase in the quantity of information being recorded, ever higher recording densities are being demanded of magnetic recording media. To achieve higher recording densities, it is necessary to reduce the size of the magnetic powder. However, the coprecipitation and reverse micelle methods present problems in that the particles sinter and aggregate during calcination, making it difficult to obtain ever finer particles.
In this regard, Japanese Unexamined Patent Publication (KOKAI) No. 2007-91517 proposes conducting calcination after coating a coprecipitate with an alkaline earth metal compound to inhibit sintering. However, based on investigation by the present inventors, the sintering-prevention effect of an alkaline earth metal compound is not necessarily adequate. A more effective means of preventing sintering is needed if higher density recording is to be achieved.